In large turbo-generators having a gas-cooled rotor winding, winding conductors are increasingly used which consist of two part conductors with E or U section which are placed on top of each other. Such a construction facilitates the mechanical machining of the winding, particularly in producing penetrations, recesses, and similar passages for supplying and removing the cooling gas (see German Patent Specification No. 11 64 564, FIG. 4, item 26).
In this arrangement, the part conductors are merely placed on top of each other. Support against centrifugal forces is provided by the slot wedge and in the lateral direction by the slot insulation.
In normal machine operation, the part conductors are pressed on top of each other due to the action of centrifugal forces in such a manner that relative movements in the peripheral direction between part conductors resting on top of each other are virtually impossible. When the shaft is rotating during cooling at low rotational speed (typically 50 revolutions per minute), in contrast, such relative movements occur which are not only capable of damaging the winding insulations but also generate abrasion of the conductor material which is distributed in the entire cooling system. Such damage to the winding insulations can impair the electric characteristics and can lead to winding or ground leakage of the rotor winding.
A material-locked bonding of the two part conductors by means of hard soldering is not possible because hard soldering would cause soft annealing of the conductor material, which is not permissible. Soft soldering, for example with the aid of thin solder foils, does not lead to any reliable bonding between the part conductors. Soldering agent emerging under full load can cause contamination of the cooling system.